Apparatus for cold rolling female threads



Jan. 13, 1953 E. TRISHMAN 2,625,055

APPARATUS FOR COLD ROLLING FEMALE THREADS Filed Dec. 16, 1950 2 SHEETS-SHEET 1 Jan. 13, 1953 AN 2,625,065

2 SHEETS-SHEET 2 Patented Jan. 13, 1953 APPARATUS FOR COLD ROLLING FEMALE THREADS Lawrence E. Trishman, Beaver, Pa., assignor to The National Supply Company, Pittsburgh, Pa., a corporation of Pennsylvania Application December 16, 1950, Serial No. 201,164

Claims.

This invention relates to cold rolling apparatus and, in particular, to apparatus for cold rolling female threads formed on a work-piece.

It is common knowledge that cold working of steel and some other metals hardens the metal, as well as forms a surface layer of metal in a state of compression, and thereby increases its fatigue resistance. Also, it is recognized that apparatus has been devised for cold rolling threads, such as the straight exterior, or male, threads of bolts and the like. However, as far as has been determined, no suitable apparatus has been provided for cold rolling and hardening to optimum fatigue resistance, female threads and, particularly, tapered female threads, such as are formed on oil well drill collars.

As to this optimum fatigue resistance, I have determined that the rolling of steel threads, and most likely threads formed of other metals, has certain limitations. Excessive rolling produces minute fissures or tears in the metal which under strain may result in a fracture emanating from such points; while insufficient cold rolling does not result in the optimum hardness. Consequently, any apparatus used for hardening threads which require this optimum must be capable of cold working the metal to a precise depth and to a depth which should not be increased or decreased even by .01" or smaller. As stated above, no suitable tapered thread working apparatus is known which is capable of such precise working of the metal.

It is therefore among the objects of this invention to provide simply constructed, easily handled apparatus for cold working female threads, the apparatus also being capable of micrometric control of the amount of metal which is worked.

. A more specific object is to provide apparatus is accordance with the above objects which, also, is capable of working the thread in such a manner that the desired thread contour is not disturbed.

According to the invention, a frame is provided for rigidly holding awork-piece, and, into the threaded end of the piece, is inserted another frame onwhich a cold-working roll is carried in a particular manner. The work-roll frame, most suitably, has a conicalportion shaped to fit into the work-piece end so as to lie a spaced distance from the thread and, also, it is provided with a longitudinally, or axially, extending track that projects in a direction parallel to the thread; this track slidably mounting a work-roll carriage and, preferably, being formed to engage and hold the carriage, as well as guide its sliding movement.

When the work-roll frame is inserted into the work-piece, the work roll is brought into engagement with the thread, or, more exactly, with the root of the thread, and from this engaged position it is necessary to feed or press the roll into the thread to the depth that it is desired for the cold working. For this purpose feeding mechanism is provided, this mechanism, generally, being adapted to press against the inserted roll frame and move it beneath or along the roll carriage, the result being that the moving frame presses against the base of the carriage and moves the roll radially outwardly into the cold-rolling engagement. With the roll so contacting the threads, cold working is performed by rotating either the work-piece or the roll frame, this rotation causing the work roll to follow the path of the thread and thereby move the roll carriage axially along its track.

Preferably, cold working is performed by stepped-increments, or, for example, the thread first may be worked to a depth of about .0025" and then the feeding mechanism operated to again, move the roll into a cold-rolling engagement that will work the thread to another .0025 on the next pass. To permit such controlled depth rolling the feeding mechanism is, most suitably, a micrometer screw that is formed to firmly engage a portion of the roll frame so that this frame can be moved in either direction to radially extend or retract the roll. Also, this firm engagement of the roll frame holds the roll positively in its set position so that it will not press further into softer metal portions of the thread, or, conversely, retract when contacting harder, uneven projections on the metal. By means of s micrometer set i s. as well as the firm control of the roll, the thread root can be cold worked any desired fractional amount and an amount that is uniform throughout the length of the thread. Other features of the invention, such as back-up means for the work roll will be described later.

The preferred embodiment of the invention is illustrated in the accompanying drawings of which Fig. 1 is an end view of the appaartus; Fig. 2 a longitudinal vertical central section showing certain elements in side elevation; Fig. 3 a transverse vertical section through the apparatus taken along the plane defined by line IIIIII of Fig. 2; and Fig. 4 an enlarged, somewhat diagrammatic illustration of the preferred manner in which the work roll engages a thread.

In the following description, the work-piece I is a section of an oil well drill collar that is provided interiorly on its end portion with a tapered steel thread 2 that previously has been hobbed to a V-shape, the root of the thread being curved or, in other words, being provided with a radius. This particular type of thread is capable of being cold worked to very high fatigue resistance as compared to square threads, or other types having angular corners which when worked have a tendency to fissure at the angular portions. However, it should be understood that the invention is not intended to be limited in its use to working any particular type of thread, or even any particular threaded member. Oil well drill collars are used to illustrate the invention simply because, as is well known, the threaded portions of such collars frequently fracture by fatigue under the reversed bending strains to which they are subjected while drilling the hole.

To hold work-piece l in position for cold working, a suitable frame 3, which may be a conventional lathe chuck, is provided, this frame being rotatable to cold roll the thread, although, as will be recognized, the apparatus can function equally well if frame 3 is held stationary and other portions rotated.

The cold working tool and its associated elements are adapted to be inserted into the thread cavity at the end of the work-piece, and to mount these members another frame 4 is provided, this frame, as shown in Fig. 2, including a conical portion e shaped to fit into the cavity and a shaft portion detachably secured to the outer face of the conical portion by means of a threaded lug 8 and bolts 9. This shaft portion normally lies outside of the thread cavity, and it is formed of a rod H having its outer end squared to receive a wrench l2 and its inner end enlarged radially to provide a flange it which forms an annular shoulder I4 that has a particular function to be described later. Inwardly of the shoulder I4, the shaft is radially reduced in size, but, nevertheless, is sufiiciently large to permit the formation of lug 8 and also to provide a surface for bolts 9.

Conical portion 5 carries work roll I 6 which performs the work on the thread, and the particular manner in which this work roll is supported, as well as the means for feeding the Work roll into cold rolling engagement with the threads form an important part of this invention. As seen in Figs. 2 and 3, work roll I6 is rotatably mounted in bearings formed in a work roll carriage ll, the carriage having side walls I8 and an enlarged base 19 the surface of which is tapered longitudinally to the same degree as the taper of the threads or, more specifically, the thread crests. The carriage is slidably mounted on a track 2! extending axially or longitudinally of conical portion 6, this track being the base of a slot formed in the conical portion. As seen in Fig. 3, side walls I 8 of the carriage engage the side walls of the slot while base 19 of the carriage fits closely into the slot base, so that the carriage is firmly secured and its sliding movement guided by the walls of the slot. Further, track [9 also is tapered to the same degree as the thread, as well as the carriage base, so that, as the carriage slides along the track, its roll remains spaced an equal distance from the thread.

To cold roll the thread, it is necessary to bring work roll I6 into cold rolling engagement with it and rotate chuck 3, this rotation causing the roll to follow the path of the thread and, consequently, to slide carriage I! along track 2|. The fact that this track is parallel to the taper of the 4 thread results in the full extent of the thread being worked uniformly.

It, also, is necessary to hold the work roll in firm, unyielding'engagement with the thread and, for this purpose a pair of steel back-up bars 22 (Fig. 3) are press fitted into axially-extending slots formed in conical portion 6 at equal circumferential distances from the axis of the work roll. These bars extend radially outwardly from the slots into engagement with the thread crests so that as the work-piece is rotated the conical portion remains centered in the thread cavity and the work roll maintains contact with the thread.

Another feature of the invention is the mechanism for feeding, or pressing, the work roll into the metal of the thread the amount by which it is desired to cold work the thread. In this regard, it should be noted that, since the roll carriage track is parallel to the taper of the thread, as the roll supporting frame is inserted into the thread cavity, the work roll eventually will come into contact with the thread. However, such contact with the thread is insufficient to efiect cold working, and it is necessary to provide mechanism for forcing the roll into the metal of the thread to the depth desired. Generally described, this mechanism is a micrometer feed screw that bears against the outer face of conical portion 6 and which, when fed toward the conical portion moves it longitudinally further into the thread cavity and, consequently, causes inclined track 2| to slide beneath the roll carriage and press the roll radially toward the thread. More specifically, the feeding mechanism includes an externally threaded, hollow-centered feed screw 23 which mounts at its outer end micrometer adjusting mechanism 24 of any conventional arrangement desired. The screw is meshed with a screw collar, or screw attaching ring 26 which, in turn, is clamped tightly onto the end of the workpiece with one of its Walls abutting the workpiec end. Further, as may be noted in Fig. 2, shaft portion I of the work roll frame projects outwardly through hollow feed screw 23, and the screw is provided at its inner end with a radially inwardly projecting flange 21 that has an inner wall engaging the outer face of conical portion 6 and an outer wall engaging shoulder 14 which, as previously stated, is formed on shaft portion 1. Consequently, when the feed screw is turned to move it toward conical portion 6 the conical portion is moved within the thread cavity and, in the manner described above, the work roll is moved radially into the thread. Conversely, when the feed screw is turned in the opposite direction, the conical portion is moved outwardly of the thead cavity due to the engagement between feed screw flange 21 and shoulder l4, and, consequently, the roll may be withdrawn radially out of engagement with the thread. To facilitate rotation of the feed screw, the outer end of the screw is provided with openings to receive a suitable tool that Will provide suificient leverage to press the work roll into the metal of the thread.

As mentioned previously, another object of the invention is to cold work the thread to an optimum fatigue resistance without disturbing the thread contour, and, for this purpose a specially formed roll is used. Thus, as may be noted in Fig. 4, the work roll is sufliciently narrower than the distance between the flanks of the thread so that the roll contacts and works only the roots of the thread and not its flanks. Thus, by way of example, if a 60 degree thread were being worked, the work roll might be 58 degrees so that its sides,

or flanks, do not contact the-flanks of the thread. It has been found, that the fatigue resistanceof the threads can be increased as much, if not more, simply by working the roots of the threads instead of working the roots and the flanks as apparently has been the previous practice. When the flanks of the thread also are worked there is a marked tendency to bend the metal and excessively distort the contour of the thread.

The operation of the apparatus has been considered to some extent in the above description, and a brief review of it should be sufficient for a complete understanding. With the work-piece firmly clamped in chuck 3, conical portion 6 of the work roll frame is inserted into the thread cavity and, with the frame inserted to a certain extent work roll it may be brought into engagement with the thread by rotating the feed screw. This initial contact between the work roll and the thread should not occur until substantially all of the conical portion is fitted into the cavity, and the amount by which the roll extends radially outwardly beyond the periphery of the conical portion may be regulated to achieve this condition. Following, or, if desired, before the positioning of the work roll within the cavity, attachment ring 26 is moved into engagement with the end of the work-piece and clamped in position. Feed screw 23 next is threaded into the attaching ring or screw collar until its inner end abuts the outer face of conical portion 6 of the work frame, following which shaft portion 1 of the work frame is secured to conical portion 6 by threading its lug into the conical portionand tightening screws 9. With shaft portion I so secured, it will be seen that shoulder 14 of the shaft portion bears firmly against flange 21 of the feed screw, flange 21 being of such a width as to effect this engagement.

The apparatus being so assembled, the work roll then is pressed into the root of the thread to the desired depth for cold rolling. In actual operation, the cold rolling of the root of the thread preferably is accomplished by making a series of traverses of the thread length and by intermittently advancing the work rolls deeper into the thread root. For instance, I have determined that steel threads of the type illustrated achieve optimum fatigue resistance if cold worked to a depth of around .01 inch and, to so work the thread, it is desirable to make successive passes, each pass working the metal to approximately .0025 inch in depth.

Inthe above description, reference has been made to the rotating of chuck 3 for effecting the cold rolling, but it may now be appreciated that, this chuck, or frame, could be stationary and work roll 4 rotated by providing suitable driving connections for rotating its shaft 1. However, if the chuck is the rotated member, it is necessary to keep the work roll frame stationary and a simple manner of accomplishing this is by blocking up wrench l2 which is mounted on the end of shaft portion 1.

The apparatus described materially improves the cold working of threads, since the amount by which the thread is worked is capable of micrometric control due to the wedging action that feeds the roll into the thread, and this control permits optimum fatigue resistance tobe achieved. Further, the tapered thread is uniformly worked and there is no distorting of the thread contour. In addition to these functional improvements, it also should be noted that the structure of the apparatus is unusually simple, inexpensive and that the apparatus as a whole is capable of' being manually assembled and oper ated wherever its need is most desired, such as in a shop at the site of an oil well.

According to the provisions of the patent statutes, I have explained the principle, preferred embodiment and mode of operation of my invention, and have illustrated and described what is now considered to represent its best embodiment. However, I desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

I claim:

1. Apparatus for cold rolling tapered thread formed interiorly on the ends of work-pieces, comprising a work-piece holding frame, a work roll formed to engage the root of said thread, a work roll carrying frame having a conical portion disposed within and spaced from the, thread of such work-piece end and a shaft portion extending outwardly of the end and provided with a shoulder, means for rotating one of said frames, said conical frame portion being provided with an axially-extending slot having a base parallel to the taper of the thread, a workroll carriage slidably mounted in said frame slot in flush contact with its tapered base, back-up bars carried by said conical frame portion, said bars extending axially of said portion and pro- Jecting radially from its periphery into contact with the crest of said thread, and work roll feeding mechanism, said mechanism including an interiorly threaded collar rigidly secured to the end portion of the work-piece, and acalibrated feed screw threadably engaged with said collar, said feed screw having an inwardly extending flange formed at its inner end, one side wall of said flange abutting said conical frame portion and the other side wall bearing against said shaft shoulder, whereby rotation of said screw in either direction moves said work roll frame and causes said work roll to move toward and away from cold rolling engagement with the root of the thread, said cold rolling being effected by rotating said one frame whereupon said work roll follows the thread and moves the roll carriage along said tapered slot to cold roll the thread uniformly.

2. Apparatus for cold rolling thread formed interiorly on the ends of work-pieces, comprising a frame for engaging and firmly holding a workpiece, a work roll frame positioned within and spaced from the thread of such a work-piece, means for rotating one of said frames, said work roll frame being provided with a track parallel to the thread, a carriage slidably mounted on said track and provided with a work roll formed to engage only the root of the thread, a back-up member comprising a plain faced backing-up bar borne by said work roll frame substantially opposite to said work roll, and mechanism borne by said work roll frame for moving said carriage longitudinally of the work-piece to adjust the work roll radially into cold rolling engagement with the root of the thread, rotation of one of said frames causing said work roll to follow the thread and move said carriage along said track to cold work the root metal of the thread uniformly.

3. Apparatus for cold rolling thread formed interiorly on the ends of work-pieces, comprising a rotatable chuck for engaging one end of and firmly holding a work-piece, a work roll frame having a, conical portion positioned within and spaced from the thread of such a work-piece and having a collar for firmly attaching the frame to the other end of the work-piece, said frame being provided with a track parallel to the thread taper, a carriage slidably mounted on said track and provided with a work roll formed to engage only the root of the thread, a back-up member comprising a plain faced backing-up bar borne by said work roll frame substantially opposite to said work roll, and mechanism borne by said collar for moving said conical frame portion longitudinally of the work-piece to adjust the work roll radially into cold rolling engagement with the root of the thread, rotation of said chuck causing said work roll to follow the thread and move said carriage along said track uniformly to cold work only the root of the thread.

4. Apparatus for cold rolling thread formed interiorly on the ends of work-pieces, comprising a rotatable chuck for engaging one end of and firmly holding a work-piece, a work roll frame having a conical portion positioned within and spaced from the thread of such a work-piece and having a collar for firmly attaching the frame to the other end of the work-piece, said frame being provided with a track parallel to the thread taper, a carriage slidably mounted on said track and provided with a work roll formed to engage only the root of the thread, a back-up member comprising a plain faced bar borne by said work roll frame substantially opposite to said work roll, an adjusting screw borne by said collar for moving said conical frame portion longitudinally of the work-piece to adjust the work roll radially into cold rolling engagement with the root of the thread, rotation of said chuck causing said work roll to follow the thread and move said carriage along said track uniformly to cold Work only the root of the thread.

5. Apparatus for cold rolling thread formed 8 interiorly on the ends of work-pieces, comprising a rotatable chuck for engaging one end of and firmly holding a work-piece, a work roll frame having a conical portion positioned within and spaced from the thread of such a work-piece and having a collar for firmly attaching the frame to the other end of the work-piece, said frame being provided with a track parallel to the thread taper, a carriage slidably mounted on said track and provided with a work roll formed to engage only the root of the thread, a back-up member comprising a plain faced bar borne by said work roll frame substantially opposite to said Work roll, an adjusting screw threadably engaging said collar and rotatably borne by said frame at the outer end of its conical portion for moving said conical frame portion longitudinally of the workpiece to adjust the work roll radially into cold rolling engagement with the root of the thread, rotation of said chuck causing said work roll to follow the thread and move said carriage along said track uniformly to cold work only the root of the thread.

LAWRENCE E. TRISHMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 794,337 Blevins July 11, 1905 1,586,238 Buckingham May 25, 1926 2,135,339 Ihm Nov. 1, 1938 FOREIGN PATENTS Nun; er Country Date 524,765 Germany May 15, 1931 

